1. Field of the Invention
The present invention relates generally to solar cells, and more particularly but not exclusively to back side contact solar cell structures and fabrication processes.
2. Description of the Background Art
Solar cells are well known devices for converting solar radiation to electrical energy. They may be fabricated on a semiconductor wafer using semiconductor processing technology. Generally speaking, a solar cell may be fabricated by forming P-type and N-type active diffusion regions in a silicon substrate. Solar radiation impinging on the solar cell creates electrons and holes that migrate to the active diffusion regions, thereby creating voltage differentials between the active diffusion regions. In a back side contact solar cell, both the active diffusion regions and the metal grids coupled to them are on the back side of the solar cell. The metal grids allow an external electrical circuit to be coupled to and be powered by the solar cell. Back side contact solar cells are also disclosed in U.S. Pat. Nos. 5,053,083 and 4,927,770, which are both incorporated herein by reference in their entirety.
Efficiency is an important characteristic of a solar cell as it is directly related to the solar cell's capability to generate power. Accordingly, techniques for increasing the efficiency of solar cells are generally desirable. Methods and structures for lowering the cost of manufacturing solar cells are also desirable as the savings can be passed on to consumers. The present invention discloses improved back side contact cell structures and fabrication processes that allow for higher efficiency and lower cost compared to conventional solar cells.